Method of operating a jet engine using fuels prepared by heating cyclo-olefins



Patented Mar. 29, 1966 This application is a divisional of applicationSerial No. 271,572, now abandoned filed April 9, 1963 for High EnergyFuels and Methods for Preparing and Using Same, which application inturn is a continuation-in-part of application Serial No. 115,317 nowabandoned, filed June This invention relates to high energy fuels whichare adapted to meet the needs of high speed modern aircraft, missilesand space vehicles, and to methods for producing and using such fuels.More particularly, the invention relates to hydrocarbon fuels capable ofmeeting high performance standards in advanced supersonic propulsionsystems and to a method for preparing such fuels in an economic mannerfrom readily available raw materials. In the ultimate aspect, theinvention relates to a method for improving the operation of jetpropulsion engines and vehicles using such engines.

Experience with many types of high energy fuels has indicated that highperformance standards may be more readily obtained with hydrocarbonfuels than with other fuels which are theoretically capable of higherperformance by virtue of higher heat content per unit weight or higherspecific impulse. However, the attainable performance depends on manyfactors besides heat content or theoretical impulse, and it is in thisarea of other chemical and physical properties that hydrocarbons showtheir advantanges and higher energy fuels their weaknesses. It has beensuggested that hydrocarbon fuels capable of meeting high performancestandards may be realized by the hydrogenation of aromatic polycyclichydrocarbons. However, it is difficult, if not impossible, to achievethe degree of hydrogenation desired by known hydrogenation procedures.

The novel high energy fuel of the invention, as described and claimed inmy above-mentioned applications, is a polycyclic hydrocarboncomposition, substantially free of olefinic unsaturation, having a heatof combustion above about 135,000 B.t.u. per gallon, a density above0.85 to 20 C., and a freezing point below about 5 C. It is prepared byFriedel-Crafts condensation of selected alkylated olefins with certaincatalysts and under special conditions.

One of the objects of the invention is to improve the performance of jetpropulsion engines through the use of the polycyclic hydrocarbon fuels,substantially free of olefinic unsaturation, prepared by the processesset forth in the aforementioned applications and also described herein.

The invention, in particular, comprises the discovery that hydrocarbonpolymers, substantially free of olefinic unsaturation, obtained byFriedel-Crafts condensation of cyclopentenes and cyclohexenes, which maypreferably have alkyl side chains of from 1 to 3 carbon atoms, areeminently suited for high energy fuels. Many experiments on thepolymerization of olefins have been reported, but the conclusions drawntherefrom have been varied and often inconsistent. It has been reportedthat when aluminum chloride reacts with alkenes not only doespolymerization take place, but also other side reactions occur such ashydroand dehydropolymerization, destructive polymerization, hydrogenredistribution and isomerization. When cyclohexene is thuslypolymerized, one is not surprised to learn that hydrocarbon polymericproducts are obtained in yields of less than 50%. Hoffman in US. Patent1,885,060 ascribed the general formula C H to olefin polymerizationproducts and found, in particular, that cyclohexene was converted into ahigher olefin such as cyclohexylcyclohexene. It has now been found thathydrocarbon polymers, substantially free of olefinic unsaturation,produced from cyclo hexene as well as from cyclopentene or itsalkyl-substituted analogs by A101 condensation, provide improved jetengine fuels by virtue of their high energy content, high specificgravity, good thermal stability, and relatively low freezing points. Ithas further been found that condensation products substantially free ofolefinic unsaturation can be produced by AlCl condensation in yields fargreater than 50% from alkyl-substituted cyclohexenes, wherein the alkylgroups comprises from 1 to 3 carbon atoms, and that such polymersprovide superior jet engine fuels by virtue of their high energycontent, high specific gravity, superior thermal stability, andrelatively low freezing points. Jet engine performance and theperformance of vehicles propelled thereby are improved by the use of thefuels described herein.

One of the preferred novel high energy fuels of this invention resultsfrom polymerizing, in the presence of aluminum chloride, cyclohexenehaving at least one alkyl substituent chosen from the group consistingof methyl, ethyl, and propyl. The polycyclic product from suchpolymcrization comprises a mixture of polycyclic hydrocarbons havingfrom 2-7 rings in the polycyclic structure, said rings each having up to7 carbon atoms and 6- membered rings being present in the mixture of anamount of about 99 mol percent; said polycyclic hydrocarbons having atleast one alkyl group of 1 to 3 carbon atoms attached to a ring carbonatom, and said polycyclic hydrocarbons being substantially free ofolefinic unsaturation. It will be understood that the novel fuel maycomprise any of the foregoing polymers separately, i.e., a polycyclichydrocarbon having a single integer number of rings in the polycyclicstructure, or a mixture of same, i.e., polycyclic hydrocarbons havingseveral integer numbers of rings in the range of 2-7 in the polycyclicstructure. Moreover, when the number of alkyl groups attached to ringcarbons is greater than one, these substituents may comprise the same ordifferent alkyl groups. Further, it is to be understood that theexpression substantially free of olefinic unsaturation does not excludea product comprising a mixture of polycyclic hydrocarbons in which oneor more of the polycyclic hydrocarbons present contains some degree ofunsaturation in the form of aromatization. However, aromatic hydrocarbonrings are present in the mixture, if at all, in a very minor amount,e.g., less than about 10 percent by weight of the total mixture.

It is also Within the scope of the invention to utilize in jetpropulsion systems fuel containing one or more of the foregoing polymerswherein the polycyclic hydrocarbons have no alkyl group attached to aring carbon. However, there is a preference for those having one alkylgroup attached to a ring carbon atom. Even more preferred are thosepolycyclic hydrocarbons having a methyl group as the one alkyl groupattached to a ring carbon atom.

Polymerization products having the general structure set forth above maybe prepared by Friedel-Crafts con densation of mono-, di-, tri-, tetra-,penta-, and hexa-alkylsubstituted cyclohexenes and mixtures thereof,preferably using AlCl A101 and HCl, AlCl and organic chlorides whichbreak down during the course of the reaction to supply HCl, AlCl /H O,and/or AlCl adducts formed during the course of a previous reaction, asthe Friedel-Crafts catalyst. Exemplitive of the various organicchlorides which supply HCl by decomposition during the course of thereaction are alkyl chlorides (e.g., ethyl chloride) and alkylcyclohexylchlorides (e.g., the chlorides formed by the addition of HCl across thedouble bond of an alkylcyclohexene). Suitable starting materials readilyobtainable are, for example, l-methylcyclohexene, 3-methylcylohexene,4-methylcyclohexene, 3,4-dimethylcyclohexene, 2,3,4-trimethylcyclohexene, and 4-ethylcyclohexene. Other representativestarting materials include l-propylcyclohexene, 3-propylcyclohexene,4-propylcyclohexene, 3-ethyl-4- methylcyclohexene, 4ethyl-l-methylcyclohexene, l-ethyl- 4-methylcyclohexene,1ethyl-3,4-dimethylcyclohexene, 4- ethyl-1,3-dimethylcyclohexene,3-methyl-4 propylcyclohexene, 1-methy-l-4-propylcyclohexene,4-methyl-1-propylcyclohexene, 1,3-dimethyl-4-propylcyclohexene, 3,4dimethyl-l-propylcyclohexene, 3,4-diethylcyclohexene, 2,3,4-triethylcyclohexene, l-ethyl 4 propylcyclohexene, 3-ethyl-4-propylcyclohexene, 3,4-diethyl-l-propylcyc-lohexene,1,3-diethyl-4-propylcyclohexene, and the like.

It has been found that unexpectedly high yields of the polymericproducts suitable for use as high energy fuels are produced from thecyclohexenes which are substituted by alkyl groups having 1-3 carbonatoms. l-alkyl, 3- alkyl, 4-alkyl-, mixtures of 3- and 4-alkyl-, andmixtures of 1, 3- and 4-alkyl-substituted cyclohexenes, in particular,provide high yields. The yields obtainable from these selected alkylatedcycloalkenes are approximately double in some instances those obtainablefrom nonalkylated cyclohexene. Thus, yields of 70% or better by weightwith respect to the weight of the starting material are obtainable withthese cycloalkenes. In general, the yield of low molecular weightmaterial in the product decreases and the yield of high molecular weightmaterial increases as the alkyl group in the starting material is movedaway from the double bond, that is, from the 1- position to the 3- tothe 4 positions.

Other polymers, substantially free of olefinic unsaturation, which aresuitable for use as high energy fuels may be produced by aluminumchloride condensation of cyclohexene, cyclopentene and alkylatedcyclopentenes. Mono-, di-, tri-, tetra-, and penta-alkylatedcyclopentenes may be utilized. While all of the foregoing polymerizationproducts provide fuels having an energy content above about 135,000B.t.u. per gallon, densities above about 0.85, and freezing points belowabout 5 C., the polymerization products from the alkylated cyclohexenesare preferred because of the relatively high yields of the end products.

cyclohexene starting materials may be readily produced by reactingethylene with a conjugated diene by processes well known in the art,e.g., by the process of US. Patents 2,349,173 and 2,349,232.Alternatively, cyclohexane and alkylated derivatives thereof may betreated to produce unsaturation in the ring structure. An example of asuitable process for producing the starting material is illustrated bythe following equation:

wherein R is hydrogen or alkyl of 1-3 carbon atoms.

In accordance with the present invention, the cyclohexenes,cyclopentenes or alkyl derivatives thereof, are polymerized in thepresence of AlCl or in the presence of AlCl and an activator orcocatalyst, at a temperature in the range of from about 5 C. to 250 C.for a period of time of from about 20 minutes to 12 hours. The reactiontime depends upon the nature of the starting materials and temperatureemployed. Preferably, the cyclic-olefin is cooled to about 0-15 C. andmixed with the catalyst whereupon the mixture is heated rapidly toreflux temperature. The reflux temperature increases as formation ofpolymeric reaction products proceeds. This temperature provides a goodindication as to the extent of the reaction. With alkylatedcyclohexenes, a reflux time of from about 20 minutes to 360 minutes hasbeen found satisfactory. In general, the reaction should be terminatedas soon as a satisfactory yield of polymerization products substantiallyfree of olefinic unsaturation is obtained. Further heating results inhigher proportions of the higher polymers. An infrared analysis of asample of the reaction mixture will provide an indication of the amountof residual unreacted cycloalkene present at a given time.

The mol ratio of cyclic olefin to aluminum chloride found to produce thedesired polymers is in the range of about 10-80 to 1. Mol ratios ofcyclic olefin to aluminum chloride of approximately 18-40 to 1 have beenfound quite satisfactory with alkylated cyclohexenes. It will beunderstood that the catalyst concentration will be as low as possibleconsistent with good yields in a reasonably short time period.

The AlCl may be activated with a small quantity of water or with ananhydrous organic chloride or hydrogen chloride gas. These materials arealso referred to as cocatalysts. In the case of water, traces sufiice.Larger quantities of water deactivate the AlCl catalyst. In the case ofHCl or organic chloride as activator or cocatalyst, the range may bevaried from traces to a molar excess in relation to the moles ofaluminum chloride, and the activating material may be addedintermittently or continuously throughly the reaction period. Asaforestated, the organic chloride is one which decomposes under thereaction conditions to form HCl. Ethyl chloride, for example, forms HCland ethylene. Alkylcyclohexyl chlorides may be used to provide HCl forcatalytic purposes and additional cyclic olefin for polymerization.

It has been found that alkylcyclohexenes form an adduct with AlCl underthe reaction conditions used. This adduct, which containsalkylcyclohexene and AlCl in a 1 to 1 molar ratio, may be separated fromthe reaction products in the form of a sludge and may be reused toprovide at least part of the AlCl catalyst for repeated reactions. Asmall amount of fresh AlCl is added as may be necessary to make upcatalyst losses and insure proper reaction conditions.

The reaction mixture may be dissolved in a suitable organic solvent suchas cyclohexane, if desired, but it is found that this is unnecessary andin some instances merely leads to separation difliculties. Higher yieldsof the cyclohexene polymerization products are, in fact, obtainedwithout the use of a solvent. Superatmospheric pressures are notnecessary. The reaction mixtures may be refluxed at atmosphericpressure.

The reaction product after completion of polymerizatron may be withdrawnfrom the reactor, water-washed and dried. In lieu of or in addition tothe water wash, the product may be given an alkali wash, e.g., with asolution of hot aqueous sodium hydroxide. However, a hot-water wash issatisfactory. Prior to the washing step, any adduct present in the formof sludge may be separated and recycled to the reaction vessel. Afterthe washing step, any unreacted cyclic olefin may be removed bydistillation and may also be recycled to the reaction vessel.

The traces of water remaining in the material after being washed may beremoved in any manner known to the art. One convenient drying processcomprises azeotropic distillation after addition of a relativelylow-boiling, nonpolar solvent such as benzene. After distillation of thebenzene/water azeotrope, distillation can be continued to removeunreacted cyclic olefins as a second fraction. Alternatively, water andunreacted cyclic olefin may be removed (without addition of benzene) byazeotropic distillation, followed by removal of any remaining unreactedcyclic olefin by distillation as a second fraction.

The product, following the treatment described above, is generally inthe form of an oil and consists of a mixture of the various polymersdescribed. These polymers may be separated into individual fractions bydistillation if desired. The individual fractions as well as themixtures provide satisfactory high energy fuel products.

The product, that is the individual fractions as well as the mixtures,exhibits certain physical properties and characteristics. The propertiesand characteristics include heats of combustion above 135,000B.t.u./gaL; densities above 0.85; high thermal stability; and lowfreezing points, below about 5 C. The preferred products of theinvention will possess heats of combustion even above 136,- 000B.t.u./gal.; densities even above 0.9; peaks in proton nuclear magneticresonance spectra at 0.905, -1.45, and -6.95; and infrared absorptionbands at wavelengths of 2740 cmr' 2690 emf- 1605 GEL-'1, 1590 cmf 1490cmr 1378 cm.- 780-790 cm.- 702 cm.'- and 750 cm.- in addition to theother properties and characteristics described in this paragraph.

When fuel storage tanks are subjected to wide diurnal variations intemperature, or when fuel chambers on vehicles are repeatedly exposed tothe low temperatures of high altitudes and the relatively hightemperatures of low altitudes, it is important that the fuels residingin such tanks or chambers undergo no loss of their original prop ertiesthrough, for example, decomposition or belated polymerization. Anotherdesirable property of the new fuels of the invention is their ability towithstand such temperature cycling without significant change in theirinitial properties.

Another aspect of the invention involves the admixture of thepolymerization products as described above with one of the elementslithium, beryllium, boron, magnesium and aluminum and/or the hydrides ofeach of these elements, to form a slurry thereof. The resulting productwill provide somewhat higher thrust when utilized in rocket propulsionengines.

The invention will be further illustrated by the following examples ofpractice.

Example 1 cyclohexene, 41 parts by weight, and cyclohexane, 42 parts byweight, were mixed and heated to 35-36 C. Aluminum chloride, 5.47 partsby Weight, was added to increments. A brown color appeared in thereaction mixture approximately 2 minutes after the first aluminumchloride was added. Heating and stirring were continued for about 3.5hours. After the first 2 hours a brown, oily liquid was observed in thebottom of the reaction flask. This layer did not grow in depth duringthe remainder of the reaction period. The reaction mixture was dissolvedin ether. There was no indication of aluminum chloride remainingunreacted in the bottom of the flask. The ether solution was washed withwater and then with 5% aqueous ferrous sulphate, acidified withsulphuric acid, to remove peroxides in the ether. The ether layer wasdried over calcium chloride and the solvents and unreacted cyclohexenedistilled from the product. The yield of oily polymeric liquid productsamounted to approximately 28% by weight of the starting cyclohexene. Itwas determined that none of the cyclohexane solvent entered into thereaction. Infrared analysis indicated that the product was substantiallyfree of olefinic unsaturation. The product had a density above 0.9, aheating value in excess of 135,000 B.t.u. per gallon, and a freezingpoint below about 5 C.

Example 2 142.5 parts by weight of 3-methylcyclohexene was mixed with63.2 parts by weight by cyclohexane as a solvent and 10.88 parts byweight of aluminum chloride was added. The mixture was heated to about98 C. and was maintained at this temperature for about 11 hours. Theproduct was then recovered as in Example 1.

The cyclohexane solvent did not enter into the reaction and infraredanalysis showed the product to be substantially free of olefinicunsaturation. The yield of the product was 86.2% by weight of the3-methylcyclohexene starting material. The product had a density of0.94, a heating value of approximately 143,000 B.t.u. per gallon, and afreezing point below 0 C. It was found to contain alkylated dimers,trimers and tetramers of the cyclohexene starting material.

Example 3 192.3 parts by weight of 4-methylcyclohexene as obtained bythe Diels-Alder reaction of butadiene and propylene was mixed with 84.2parts by weight of cyclohexane as a solvent and with 14.5 parts byweight of aluminum chloride. The mixture was heated to C. (the refluxtemperature at atmospheric pressure) and was maintained at refluxtemperature for approximately 10.5 hours. The product oil was thenrecovered as before. Its infrared spectrum showed absorption bands atwavelengths of 2740 cm.'" 2690 crnf 1605 cm. 1590 cm. 1490 cm. 1378 cm.780-790 cm. 702 cmf and 750 cm. Its proton nuclear magnetic resonancespectrum showed peaks at 0.905, -1.46, 2.36, and -6.95. The yield Was72% by Weight of the starting material, the product containing dimer,trimer and higher boiling fractions. Of the converted material, about 5%was the dimer. The density of the product was 0.979 at 20 C., the heatof combustion approximately 149,000 B.t.u. per gallon and the freezingpoint below about 5 C. This product was outstanding from the viewpointof high energy fuel properties and high yield from readily avail ablestarting material.

Proton nuclear magnetic resonance spectra in this and all other exampleswere obtained from a Varian Associates A60 spectrometer operating at 60m./sec. Spectra were calibrated on the 5 scale with tetramethylsilane asan internal reference.

Example 4 The procedure of Example 3 was repeated, again utilizing4-methylcyclohexene, except that the reaction time was reduced to 1.5hours. The conversion was increased to 76%, with the yield of dimerincreasing to 10% and the trimer yield to 18%, the remainder beinghigher boiling fractions. The density, heat of combustion, and freezingpoint for this product remained about the same as that produced by theprocedure of Example 3.

Example 5 The procedure of Example 4 was repeated, utilizing4-methylcyclohexene, and a 1.5 hour reaction time, but without the useof cyclohexane as a solvent. The yield increased to 83%, with the yieldof the dimer increasing to 17% and the trimer decreasing to 14%, withthe remainder being higher boiling fractions. The density and heat ofcombustion were not reduced. The freezing point remained below about 5C.

Example 6 A mixture of 192.3 parts by weight of 3-methylcyclohexene and4-methylcyclohexene was mixed with 84.2 parts by weight of cyclohexaneas a solvent and 14.5 parts by weight of aluminum chloride were added.The reaction mixture was heated to 90 C. and maintained at approximatelyreflux temperature for about 11 hours. The product was then recovered asbefore and was found to contain a mixture of dimer, trimer and higherboiling fractions in a yield of about 93%. Infrared analysis showed theproduct to be substantially free of olefinic unsaturation. The producthad a density of 0.95 at 20 C., and a heating value of about 145,000B.t.u. per gallon.

The following table provides a comparison of the process conditions andproduct results from the foregoing examples, as well as from additionalexamples utilizing l-methylcyclohexene, cyclohexene and cyclopentene:

pure grade cyclohexane, and (3) 72.5 parts of Baker Analyzed Gradeanhydrous aluminum chloride were M01 ratio solvent Conversion, Heating,Freezing Example Cyclioolefin cyclic-olefin Time, Temp, percent Densityvalue, not point, No. to A101; fiillgelfiltliittz) min. C. by wt. at 20C. Btu/gal. C.

Name ei clieolefin Cyclohexene Cyclohexane. l 213 35 28 0. 9 135, 000 58-methylcyclohexene .do .1 0.50 650 98 S6 0. 94 143, 000 54-rnethyleycl0hexene 0. 5 650 90 72 0. 979 149, 000 5 0.5 90 90 76 0.970149,000 d0 None 90 40-138 83 0. 970 149,000 5 3- and 4-methyleyclo- 0. 5050 91 93 0.95 145, 000 5 cg ffli e x ene 18.3 do 0.5 650 79 36 0.945142,000 '6&i o ii thII .IIl i313 dgfaah'ah i hit; 223 79 3% it 833%;ittjidt 2E l-methylcyclohexene 18.3 Cyclohexane 0.5 630 97 78 0.917139,000 5 1 Freezing point determination by A.S.T.M. Method D-1477-57'1.

Example 11 mixed and heated at reflux for 5.7 hours. The reaction dflmth1c clohexene was cooled to c b an mixture was cooled to room temperatureby an ice-water ternal icewai ter bath. Anhydrous aluminum chlo r idewas bath 9 parts of fithyl ethfr was addsd' After the then added in theratio of 1 mole Alclg to 40 moles of reaction mixture had dissolved inthe ether, 1250 parts the cycloalkene, and anhyldrous HCl was passedinto the of.dlstllled Water was Slowly to hydroly. Cool mixture for oneminute External cooling was minum ChlOIldS. After several minutes ofbeing stirred, Placed by heating and the temperature of the mixture wasconlfients of the flask Ware Placed m a separatory raised rapidly toreflux, 98 C. As the reaction proceeded, T i g pllase W removed and theether 9 the temperature of the reflux increased, during about 23 l Was 6twice Wlth a 2000 parts of acldl' minutes, to about 148 C., due toformation of the dimer, aqueous ferrouf Sulfate Solunon' The .gtherlayfir trimer, and higher polymers. Heating was then discon- W thanWashed F three looo'part portions of dls' tinued. The total time for thereaction, including time fined Water A Bsllstem test was l p f etherlayer in heating to reflux, was 38 minutes. The hot mixture was and nogreen flame was Obsrvad lndlcanng the absgnce filtered through asintered glass filter to recover a major chlorlllne or the presence fless than 5 of part of the sludge content. This sludge was analyzed andg T e ether layfapwas dned Over anhydrous alumina, found to be a4-methy1cycl0hexene/AlCl adduct in 1 t0 1 grad and then distilled toremove ether cycloilexane ratio. The adduct was reused to supply AlClfor a furand unreacted olefins' (:omierslon was approxlmatlly therreaction with additional 4-methylcyclohexene. The The Product a amixture of polymers the i filtrate was washed 7 times with portions ofhot water frfiared spicltrum of jf Showed Bi at 9 each equal in volumeto that of the filtrate, to remove 2 9 1605 2 1590 4 1490 4 1378 anysludge and/or AlCl which passed through the 111- 40 780790 702 and 750tration step. Traces of water remaining in the layer of ton Showed Peaksat 06, -1.46, 2.35, and organic material were removed by the addition ofa small volume of dry benzene followed by distillation of the mix-Dlsnllanon of the P 15mg a Vlgreux ture to provide a first distillationfraction comprising a ylelded the followmg component parts:benzene/water azeotrope. Distillation was continued until the remainingbenzene and all unconverted 4-methyl- Boiling range 0 C.) cyclohexenewere removed. The residual fraction in the Number of rings Pressure potof the distillation apparatus consisted of a high en- Initial Final (mm)ergy fuel having substantially the same properties as set forth inExamples 3, 4 and 5 of the table' 2 (dimer) 105-110 150 N1 In analternative operation, water was removed by dis- 3(trin1er) 150 205tilling the wet product from the water wash without the 205 N1 additionof benzene. The first fraction was an azeotrope insisting of unconverted4'methY1CyC10heXene and Water- The infrared spectrum of each of thecomponents showed Further distillation removed the remainder of theunreb d at 2740 2690 cmrl, 1605 cmfl, 1599 1 acted cyclic olefin. Totalconversion of starting material 1490 1 1373 1 7g 7 1 702 -1 andfimountfid to about 79% in these procedures- 750 cm. Proton n.m.r. ofeach showed peaks at 0.905,

Examp 1e 12 iii? iii; and 3 1 bt d d th th o e pro uc s o aine 1n accorance W1 e The reactlon Procedure Example i i procedures set forth in theforegoing examples and table except m no Hcl was m? Dyed and t e A can Yare Well suited for high energy fuels for supersonic air- Wasacnvatedhby thefaddltlwtl of Y 3 2 f g craft. The products obtained bypolymerization of the or proximately 80 C. and heating was continued fora period gi g f i gi g igii g ffig z fi g gf ggg of 90 minutes until areflux temperature of 172: was 4 methylcyclohexene in Examples was 83%as reached. The reaction product was worked up as in thle pared to a 44%yield from nonalkylated cyclohexene Precedmg eXamP 1e- Conversion of the4'methy acted under approximately the same conditions (ExampleCyclohexene startmg mater1a1Wa573-5%- s of the table). The yield fromthe mixed 3- and 4- Example 13 methyl isomers of cyclohexene was above90%. It is apparent, therefore, that yields obtainable from the (1)961.5 parts of a mixture of olefins comprising alkylated products arealmost double those obtainable 773.0 parts of 4-methylcyclohexene, 183.7parts of 3- from the parent compound. This result was quiteunexmethylcyclohexene, 2.9 parts of l-methylcyclohexene, and pected andrepresents a discovery of considerable eco- 1.9 parts ofrnethylenecyclohexane, (2) 421.0 parts of nomic importance. Other alkylsubstituents, such as ethyl, propyl, and isopropyl, may be used on thecyclohexene ring structure to the same advantage.

The high energy hydrocarbon fuels of the present invention areparticularly suitable for use in jet propulsion systems includingramjet, turbo-jet and tunbo-prop engines. The method of operating suchjet engines according to the invention comprises feeding the combustionchamber of the engine with an oxidizing agent and with a polycyclichydrocarbon fuel, substantially free of olefinic unsaturation, resultingfrom the Friedel-Crafts polymerization of a cyclo alkene includingcyclopentene, cyclohexene, alkyl-substituted cyclopentene,alkyl-substituted cyclohexene and mixed isomers of such alkylsubstitutedcompounds, subjecting the resulting mixture of fuels and oxidizing agentto combustion and passing the resulting hot gases into the atmospherethrough a nozzle to produce thrust. The oxidizing agent may comprise airwhich has been compressed from the atmosphere or other oxidant. In theinstance in which the jet engine is a turbo-jet, the combustion gasesare expanded through a turbine prior to passing through the nozzle. Itwill be understood that the ratios of fuel to oxidizing agent will beselected to meet the performance requirements of the particular engine,depending upon the load at the time.

It has also been found that improved results from the standpoint of highimpulse for rocket engines may be obtained by admixing such substancesas lithium, beryllium, boron, magnesium, and aluminum, and/or thehydrides of these substances, with the fuels of the invention to form aslurry. The viscosity of the fuels of the invention facilitatesmaintaining of the slurried materials in suspension to provide a stablemixture. These mixtures also have the desirable property of high thermalstability.

It will be readily apparent to those skilled in the art that manychanges and variations of the invention may be made without departingfrom the spirit thereof.

I claim:

1. A method of operating a jet engine, comprising: feeding thecombustion chamber of said engine with an oxidizing agent and with ahydrocarbon fuel containing polycyclic compounds substantially free ofolefinic unsaturation obtained by heating a cycle-olefin substanceselected from the group consisting of cyclopentene, cyclohexene,alkyl-substituted cyclopentene, alkyl substituted cyclohexene, and mixedisomers of said alkyl substituted compounds with aluminum chloride untila condensate having a density above 0.85 and a heat of combustion above135,000 B.t.u. per gallon is formed, subjecting the resulting mixture offuel and oxidizing agent to combustion and passing the resulting hotgases through a nozzle to produce thrust.

2. The method of claim 1 wherein the polycyclic hydrocarbon fuel isobtained by heating cyclopentene with aluminum chloride until acondensate having a density above 0.85 and a heat of combustion above135,000 B.t.u. per gallon is formed.

3. The method of claim 1 wherein the polycyclic hydrocarbon fuel isobtained by heating an lalkylasmbstituted cyclohexene with aluminumchloride until a condensate haivng a density above 0.85 and a heat ofcombustion above 135,000 B.t.u. per gallon is formed.

4. The method of claim 1 wherein the polycyclic hydrocarbon fuel isobtained by heating a mixture of 3-methyland 4-methylcyclohexenes withaluminum chloride until a condensate having a density above 0.9 and aheat of combustion above 140,000 B.t.u. per gallon is formed.

References Cited by the Examiner UNITED STATES PATENTS 2,927,849 3/1963Greblick et al. 149-87 X 3,105,351 10/1963 Stahy -354 3,113,419 12/1963Koch 6035.4 3,1 13,420 12/1963 Wineman 6035.4 3,113,421 12/1963 Koch60-35.4 3,113,422 12/1963 Wineman 60-35.4 3,126,330 3/1964 Zimmerschiedet a1. 60-35.4 X 3,128,596 4/1964 Morris 60-35.4

BENJAMIN R. PADGETT, Acting Primary Examiner.

CARL D. QUARFORTH, Examiner.

1. A METHOD OF OPERATING A JET ENGINE, COMPRISING: FEEDING THECOMBUSTION CHAMBER OF SAID ENGINE WITH AN OXIDIZING AGENT AND WITH AHYDROCARBON FUEL CONTAINING POLYCYCLIC COMPOUNDS SUBSTANTIALLY FREE OFOLEFINIC UNSATURATIN OBTAINED BY HEATING A CYCLO-OLEFIN SUBSTANCESELECTED FROM THE GROUP CONSISTING OF CYCLOPENTENE, CYCLOHEXENE,ALKYL-SUBSTITUTED CYCLOPENTENE, ALKYL SUBSTITUTED CYCLOHEXENE, AND MIXEDISOMERS OF SAID ALKYL SUBSTITUTED COMPOUNDS WITH ALUMINUM CHLORIDE UNTILA CONDENSATE HAVING A DENSITY ABOVE 0.85 AND A HEAT OF COMBUSTION ABOVE135,000 B.T.U. PER GALLON IF FORMED, SUBJECTING THE RESULTING MIXTURE OFFUEL AND OXIDIZING AGENT TO COMBUSTION AND PASSING THE RESULTING HOTGASES THROUGH A NOZZLE TO PRODUCE THRUST.